Change your existing/saved SVN user to other user on your UNIX machine or MAC OSx

Locate and find your .subversion directory, mostly it will under your home directory.

.subversion/auth/svn.simple/random-numbered-file ( without extension )

for eg ( in my machine ) :

Jackys-MacBook:svn.simple gokulamurthy$ ls
772c71669d28a02d42addb1d967d1862
Jackys-MacBook:svn.simple gokulamurthy$ vi 772c71669d28a02d42addb1d967d1862

K 8
passtype
V 8
keychain
K 15
svn:realmstring
V 42
SVN Access
K 8
username
V 14
your-existing-svn-username
END

change your existing svn username to current username then save and close the file.

when you do any operation under your subversioned directory like svn ls , svn log, svn up, svn switch, etc., for any operations it will ask you enter the svn new username and password.

Thats all. Have Fun with SVN.